CN112505182B - Py-GC/MS analysis method for micro-plastic in agricultural soil - Google Patents
Py-GC/MS analysis method for micro-plastic in agricultural soil Download PDFInfo
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Abstract
The invention discloses a Py-GC/MS analysis method of micro-plastics in agricultural soil, wherein the micro-plastics are PE and PVC, and the Py-GC/MS analysis method comprises the following steps: (1) Taking a soil sample to be detected, and adding H with the volume concentration of 1-30 percent 2 O 2 Taking the aqueous solution as a digestion solution, digesting at 30-70 ℃, heating and drying to remove the residual digestion reagent and generated water after the reaction is completed, placing the sample in a mortar after digestion, and grinding into powder for later use; (2) Obtaining a Double-Shot-Py-GC/MS total ion flow graph of the soil sample with the cracking temperature of 320-380 ℃ and 450-600 ℃ by adopting a Double-Shot cracking-gas chromatography/mass spectrometry combined method for the soil sample digested in the step (1); (3) And (3) carrying out qualitative and/or quantitative analysis by using the Double-Shot-Py-GC/MS total ion flow graph of the soil sample obtained in the step (2). The method can avoid the loss of the sample in the density separation step, has no requirements on the size, the color and the density of the micro-plastics, can simultaneously measure the content of various types of micro-plastics in agricultural soil, and has good reproducibility and accuracy.
Description
Technical Field
The invention relates to a cracking-gas chromatography/mass spectrometry combined analysis method (Py-GC/MS) for micro-plastics in agricultural soil.
Background
Microplastic (MP) is a plastic with a diameter of less than 5mm, and common types of MP are: polyethylene (PE), polyvinyl chloride (PVC), polyethylene terephthalate (PET), polypropylene (PP), ethylene-vinyl acetate copolymer (EVA), polystyrene (PS), polycarbonate (PC). The sources of micro-plastics in soil are mainly: the use of agricultural mulching films, the irrigation of waste water, the landfill of garbage and the settlement of atmosphere, especially the accumulation of agricultural plastics (mulching films, PE, PVC and the like) in soil, and the pesticide which is rich on the surface of the plastics and harmful substances contained in the plastics influence the survival of soil organisms and plants, thereby becoming a novel pollution source in the soil.
Most of published MP literature researches are focused on ocean and fresh water, the pretreatment needs to be performed by complex operations such as drying, screening, floating, filtering, density separation, digestion and the like, so that samples which can be detected by using a given selection method are limited, various types of MP plastics are difficult to analyze, the MP plastics are limited by different factors, and the research on micro plastics in soil is few. Therefore, there is an urgent need to develop a method for separating and identifying MP to reflect the actual soil pollution status. As the retention time of different types of MP thermal cracking products in chromatographic columns is similar and the separation degree is too small, the method adopts Double-Shot-Py-GC/MS analysis technology to achieve the purpose of measuring different types of MP by cracking the MP at different temperature points.
Disclosure of Invention
The invention aims to provide a simple and rapid analysis technology for simultaneously carrying out qualitative and quantitative analysis on micro-plastics in soil of an agricultural land.
In order to solve the technical problem, the technical scheme adopted by the invention is as follows:
a Py-GC/MS analysis method for micro plastics in agricultural soil, wherein the micro plastics are PE and PVC, and the Py-GC/MS analysis method comprises the following steps:
(1) Digestion of soil sample to be tested
Taking a soil sample to be detected, and adding H with the volume concentration of 1-30 percent 2 O 2 Taking the aqueous solution as a digestion solution, digesting at 30-70 ℃, heating and drying to remove the residual digestion reagent and generated water after the reaction is completed, placing the sample in a mortar after digestion, and grinding into powder for later use;
(2) Double-click pyrolysis-gas chromatography/mass spectrometry (Double-Shot-Py-GC/MS)
Putting the soil sample digested in the step (1) into a sample cup, covering a layer of quartz cotton on the sample, fixing the sample cup on a sample introduction rod, loading the sample cup into a cracker, wherein the cracking temperature is 320-380 ℃, pushing down the sample introduction rod after the instrument is stabilized, enabling the sample cup to enter a heating zone of the cracker, and simultaneously starting a gas chromatograph to perform GC/MS analysis to obtain a Double-Shot-Py-GC/MS total ion flow graph of the soil sample at the temperature of 320-380 ℃; after the analysis is finished, lifting the sample cup, heating the cracker to 450-600 ℃, pushing down a sample rod after the instrument is stabilized, enabling the sample cup to enter a heating zone of the cracker, and simultaneously starting a gas chromatograph GC/MS (gas chromatography/mass spectrometry) for analysis to obtain a Double-Shot-Py-GC/MS total ion flow graph of the soil sample at 450-600 ℃;
Double-Shot-Py-GC/MS instrument conditions:
the instrument comprises the following steps: GCMS-QP2010SE gas chromatography-mass spectrometer; a cracker: the first stage is 320-380 deg.C, and the second stage is 450-600 deg.C; cracker/GC interface temperature: 300-320 ℃; sample inlet temperature: 300-320 ℃; and (3) chromatographic column: rtx-5MS capillary chromatography column (30 m × 0.25mm i.d. × 0.25 μm,5% phenyl-95% polydimethylsiloxane); when the cracking temperature is 320-380 ℃, the temperature programming condition is as follows: maintaining the temperature at 40 deg.C for 2min, heating to 100 deg.C at 10 deg.C/min, maintaining for 10min, heating to 320 deg.C at 20 deg.C/min, and maintaining for 15min; when the cracking temperature is 450-600 ℃, the temperature programming condition is as follows: maintaining at 40 deg.C for 2min; heating to 320 ℃ at a speed of 20 ℃/min, and keeping for 15min; the split ratio is as follows: 30-50:1; the carrier gas is high-purity helium, and the column flow is as follows: 1mL/min; an ion source: EI; ion source temperature: 220 to 250 ℃; transmission line temperature: 250 ℃; electron energy 70eV; scanning mode: full scanning; scanning period: 0.5s; scanning range: m/z:50-600amu;
(3) Performing qualitative and/or quantitative analysis by using Double-Shot-Py-GC/MS total ion flow graph of the soil sample obtained in the step (2)
(1) Qualitative analysis
If characteristic peaks of benzene and naphthalene appear on the Double-Shot-Py-GC/MS total ion flow chart of the soil sample at 320-380 ℃ obtained in the step (2), the soil sample contains PVC; if the Double-Shot-Py-GC/MS total ion flow graph of the soil sample at 450-600 ℃ obtained in the step (2) has characteristic peaks of C19, C20, C21 and C22, wherein Cn represents a hydrocarbon peak cluster with the carbon atom number n, and the soil sample contains PE;
(2) quantitative analysis
Preparing a series of mixed standard soil samples containing PE and PVC with concentration, and respectively obtaining a Double-Shot-Py-GC/MS total ion flow graph of the mixed standard soil samples at 320-380 ℃ and 450-600 ℃ according to the operations in the steps (1) and (2); taking the concentration of PE in the mixed standard soil sample as a horizontal coordinate, taking the peak areas of PE characteristic cracking products C19, C20, C21 and C22 in a Double-Shot-Py-GC/MS total ion flow graph of the mixed standard soil sample at 450-600 ℃ as a vertical coordinate to establish a standard curve, substituting the peak areas of C19, C20, C21 and C22 of the soil sample to be detected obtained in the step (2) into the standard curve to respectively obtain the PE concentrations obtained according to C19, C20, C21 and C22, and taking the average value of the four as the PE concentration in the soil sample to be detected; and (3) establishing a standard curve by taking the concentration of PVC in the mixed standard soil sample as a horizontal coordinate and taking the peak areas of the PVC characteristic cracking products benzene and naphthalene in the Double-Shot-Py-GC/MS total ion flow graph of the mixed standard soil sample at 320-380 ℃ as a vertical coordinate, substituting the peak areas of the benzene and the naphthalene of the soil sample to be detected obtained in the step (2) into the standard curve to respectively obtain the PVC concentrations obtained according to the benzene and the naphthalene, and taking the average value of the two concentrations as the PVC concentration in the soil sample to be detected.
In the invention, before the soil sample is digested, the soil sample is preferably pretreated: selecting large particle impurities such as residual plants, drying to remove water, grinding, and sieving.
In step (1) of the present invention, H 2 O 2 The concentration of the digestion solution is an important factor affecting the digestion efficiency. H 2 O 2 The concentration of (2) is too high, PE in soil can be dissolved, and subsequent quantitative analysis is influenced; h 2 O 2 Too low a concentration may result in incomplete digestion of organic matter in the soil, and the cracked product of the soil organic matter interferes with analysis of the MP-characteristic cracked product. Preferably, H 2 O 2 The volume concentration of the digestion solution is 5%, the PE is slightly influenced at the moment, and the digestion of organic matters in the soil is complete.
In the step (1) of the invention, H is promoted when the digestion reaction temperature is too high 2 O 2 The solution can not completely digest PE when the content of PE is too low. Preferably, the digestion temperature is 30 ℃, organic matters in the soil are basically completely digested at the time, the response signal of the cleavage product is low, and the MP cleavage product analysis is slightly influenced. The digestion time directly reflects the simplicity and convenience degree and the experimental efficiency of the pretreatment, and the preferred digestion time is 20min.
Particularly preferred according to the invention is step (1), wherein H 2 O 2 The volume concentration of the aqueous solution is 5%, the digestion temperature is 30 ℃, and the digestion time is 20min.
In step (3) of the present invention, the single-standard soil sample is preferably prepared by an equivalent soil dilution method: and (3) putting the micro plastic particles and the same amount of blank soil into a mortar, grinding and uniformly mixing, adding a blank soil sample with the same amount as the sample in the mortar, grinding and uniformly mixing, gradually adding a blank soil sample with the same amount as the mixture in the previous mixing step, grinding and uniformly mixing, and finally preparing a series of single-standard soil samples with the concentration. The mixed standard soil sample can also be prepared by a similar method, and the preferable preparation method of the mixed standard soil sample is as follows: and (2) putting polyvinyl chloride (PVC) particles and equal amount of blank soil into a mortar, grinding and uniformly mixing, adding Polyethylene (PE) particles into the mortar, grinding and uniformly mixing, adding a blank soil sample which is equal to the sample in the mortar, grinding and uniformly mixing, gradually adding a blank soil sample which is equal to the mixture obtained in the previous mixing step, grinding and uniformly mixing, and finally preparing to obtain a series of mixed standard soil samples with concentration. The preparation method of the single-standard and mixed-standard soil samples can improve the uniformity of the samples and is beneficial to obtaining more accurate results in later detection.
In the present invention, the preferred Double-Shot-Py-GC/MS instrument conditions are:
cracker (Japanese Py-3030D vertical micro furnace): the first stage is 380 ℃ and the second stage is 600 ℃; cracker/GC interface temperature: 320 ℃; sample inlet temperature: 320 ℃; a chromatographic column: rtx-5MS capillary chromatography column (30 m × 0.25mm i.d. × 0.25 μm,5% phenyl-95% polydimethylsiloxane); when the cracking temperature is 380 ℃, the temperature programming condition is as follows: maintaining the temperature at 40 deg.C for 2min, heating to 100 deg.C at 10 deg.C/min, maintaining for 10min, heating to 320 deg.C at 20 deg.C/min, and maintaining for 15min; when the cracking temperature is 600 ℃, the temperature programming condition is as follows: maintaining at 40 deg.C for 2min; heating to 320 deg.C at 20 deg.C/min, and maintaining for 15min; the split ratio is as follows: 50:1; the carrier gas is high-purity helium, and the column flow is as follows: 1mL/min; an ion source: EI; ion source temperature: 220 ℃; transmission line temperature: 250 ℃; electron energy 70eV; scanning mode: full scanning; scanning period: 0.5s; scanning range: m/z:50-600amu.
Compared with the prior art, the invention has the advantages that: the loss of samples in the density separation step can be avoided, the requirements on the size, the color and the density of the Micro Plastic (MP) are not required, and the uncertainty caused by human errors when the micro plastic is manually selected is also avoided. The content of various types of micro-plastics in agricultural soil can be simultaneously determined in a Double-Shot cracking mode, the repeatability and the accuracy are good, and the analysis method of the micro-plastics in the soil by using Py-GC/MS is perfected.
Drawings
Fig. 1 is an EGA graph of digested soil samples, polyethylene (PE), polyvinyl chloride (PVC) single scale soil samples.
FIGS. 2-a and 2-b: the total ion flow diagrams of single-scale soil samples of Polyethylene (PE) and polyvinyl chloride (PVC) at 380 deg.C (FIG. 2-a) and 600 deg.C (FIG. 2-b), respectively.
FIGS. 3-a and 3-b: respectively, a Double-Shot-Py-GC/MS total ion flow diagram of Polyethylene (PE) and polyvinyl chloride (PVC) mixed standard soil samples at 380 ℃ (figure 3-a) and 600 ℃ (figure 3-b).
Figure 4 shows the effect of digestion solution concentration on digestion of soil organic matter and on micro-plastic depletion, where a: response plots of soil lysates; b: PVC cleavage product response graph; c: PE cleavage product response plot.
Figure 5 shows the effect of digestion temperature on digestion of soil organic matter and on micro-plastic depletion, where a: response plots of soil lysates; b: PVC cleavage product response graph; c: PE cleavage product response plot.
Figure 6 shows the effect of digestion time on digestion of soil organic matter and on micro-plastic depletion, where a: response plots of soil lysates; b: PVC cleavage product response graph; c: PE cleavage product response plot.
Detailed Description
The invention will be further described with reference to specific examples, but the scope of the invention is not limited thereto.
Example 1
(1) Preparation of soil samples
Selecting large particle impurities such as residual plants from a blank soil sample mesh, drying at 100 ℃ for 3h to remove water, grinding, and sieving for later use;
preparing a single-standard soil sample by an equivalent soil dilution method: taking Polyethylene (PE) particles and equal amount of blank soil into a mortar, grinding and uniformly mixing, then adding equal amount of blank soil samples to the mortar, grinding and uniformly mixing, successively adding equal amount of blank soil samples to the mixture obtained in the previous mixing step, grinding and uniformly mixing, and finally preparing PE single-standard soil samples with PE mass concentrations of 1% and 0.05%; taking polyvinyl chloride (PVC) particles, preparing a PVC single-standard soil sample with the mass concentration of 0.50 percent and 0.05 percent by using the equivalent soil dilution method for later use;
preparing a mixed standard soil sample by an equivalent soil dilution method: taking polyvinyl chloride (PVC) particles and equal amount of blank soil in a mortar, grinding and uniformly mixing, adding Polyethylene (PE) particles in the mortar, grinding and uniformly mixing, then adding a blank soil sample with equal amount of the sample in the mortar, grinding and uniformly mixing, successively adding a blank soil sample with equal amount of the mixture in the previous mixing step, grinding and uniformly mixing, and finally preparing a mixed standard soil sample with the mass concentrations of PVC and PE of 0.50 percent and 2.00 percent respectively;
(2) Digestion of samples
Weighing 500.00mg of the single-standard soil sample and mixed-standard soil sample prepared in step (1) into sample bottles, adding 5.0mL of the soil samples into the sample bottles, and adjusting the content to 5% H 2 O 2 Digesting the solution at 30 ℃, reacting for 20min, heating to 100 ℃, drying for 5h, and removing the residual digestion reagent and the generated water. After digestion, the sample is put into a mortar and ground into powder for later use.
(3) Analysis of Evolved Gas (EGA)
Weighing 20.00mg digested PE single standard soil sample with the mass concentration of 0.05 percent and 0.05 percent PVC single standard soil sample into a sample cup, covering a layer of quartz wool on the sample, fixing the sample cup on a sample injection rod, loading the sample cup into a cracker, pressing a sample injection button after the instrument is stabilized, enabling the sample cup to rapidly fall into a heating zone of the cracker, simultaneously starting a gas chromatograph to analyze the Escaping Gas (EGA) and determining the change of the thermal stability along with the temperature, wherein the result is shown in figure 1, the mixture of PE and soil is cracked in a one-stage mode, the cracking temperature is 380-500 ℃, the mixture of PVC and soil is cracked in a two-stage mode, and the cracking temperatures are respectively 250-380 ℃ and 380-600 ℃.
EGA test conditions: the instrument comprises the following steps: gas chromatograph (Thermo Scientific TRACE GC ULTRA), cracker (Frontier PY-3030D); temperature programmed condition of the cracker: the initial temperature is 100 ℃, and the temperature is raised to 700 ℃ at 20 ℃/min; cracker/GC interface temperature: 300 ℃, injection port temperature: 300 ℃; deactivating the uncoated stainless steel capillary (0.15 mm. Times.2 m); the split ratio is as follows: 50; column temperature: keeping at 300 deg.C for 30min; FID detector temperature: 300 ℃; the carrier gas is high-purity nitrogen, and the column flow is as follows: 1mL/min.
(4) Double-click pyrolysis-gas chromatography/mass spectrometry (Double-Shot-Py-GC/MS)
According to the analysis result of the single-label soil sample escaping gas curve shown in the figure 1, the PE and PVC mixed sample can be subjected to segmented cracking at different temperatures by using a Double-Shot-gas chromatography/mass spectrometry (Double-Shot-Py-GC/MS). Characteristic cleavage products of PE and PVC were sought.
Respectively weighing 20.00mg of digested single-standard soil sample with the mass concentration of PE 1% and single-standard soil sample with the mass concentration of PVC 0.5% in a sample cup, covering a layer of quartz wool on the samples, fixing the sample cup on a sample injection rod, loading into a cracker, the cracking temperature is 320-380 ℃, pushing down the sample injection rod after the instrument is stable, enabling the sample cup to enter a heating zone of the cracker, simultaneously starting a gas chromatograph for GC/MS analysis, lifting the sample injection cup after the analysis is finished, heating the cracker to 450-600 ℃, pushing down the sample injection rod after the instrument is stable, enabling the sample cup to enter the heating zone of the cracker, and simultaneously starting the gas chromatograph for GC/MS analysis, wherein the results are shown in figures 2-a and 2-b.
Double-Shot-Py-GC/MS instrument conditions: the instrument comprises the following steps: GCMS-QP2010SE gas chromatography-mass spectrometer (Shimadzu corporation, japan); cracker (japanese Py-3030D vertical micro furnace): the first stage is 380 ℃ and the second stage is 600 ℃; cracker/GC interface temperature: 320 ℃; sample inlet temperature: 320 ℃; a chromatographic column: rtx-5MS capillary chromatography column (30 m × 0.25mm i.d. × 0.25 μm,5% phenyl-95% polydimethylsiloxane); when the cracking temperature is 380 ℃, the temperature programming condition is as follows: maintaining the temperature at 40 deg.C for 2min, heating to 100 deg.C at 10 deg.C/min, maintaining for 10min, heating to 320 deg.C at 20 deg.C/min, and maintaining for 15min; when the cracking temperature is 600 ℃, the temperature programming condition is as follows: maintaining at 40 deg.C for 2min; heating to 320 deg.C at 20 deg.C/min, and maintaining for 15min; the split ratio is as follows: 50:1; the carrier gas is high-purity helium, and the column flow is as follows: 1mL/min; an ion source: EI; ion source temperature: 220 ℃; transmission line temperature: 250 ℃; electron energy 70eV; scanning mode: full scanning; scanning period: 0.5s; scanning range: m/z:50-600amu.
(5) Selection of characteristic peaks of MP
As can be seen from FIG. 2-a, when the cracking temperature is 320-380 ℃, the first stage cracking of PVC occurs, benzene and naphthalene escape, and PE is not cracked yet, so that the benzene and naphthalene can be determined to be the characteristic cracking products of PVC; when the cracking temperature is 450-600 ℃, the two are cracked simultaneously, the cracking products of the mixture of PVC and soil in figure 2-b respectively comprise benzene, toluene, hexylbenzene, o-xylene, methylindene, naphthalene, methylnaphthalene and anthracene, and the retention time is less than 12.2min. The PVC cleavage products interfere with the analysis of the PE cleavage products within 0-12.2min, and C19, C20, C21 and C22, which have a larger response signal and a retention time of 12.43, 12.94, 13.42 and 13.89min, respectively, are selected as characteristic cleavage products of PE in the apparatus, see FIG. 2-b, where Cn represents a hydrocarbon peak cluster with the number of carbon atoms n.
(6) Testing of mixed-standard soil products
Weighing 20.00mg of mixed standard soil sample digested in the step (1) in a sample cup, performing Double-click cracking-gas chromatography/mass spectrometry analysis according to the operation of the step (4), wherein the graphs in figures 3-a and 3-b are total ion flow graphs of PVC and PE mixed standard soil samples (Double-Shot-Py-GC/MS), and as can be seen from the graphs, characteristic products (benzene and naphthalene) are cracked by PVC at the cracking temperature of 320-380 ℃, characteristic products (C19, C20, C21 and C22) are cracked by PE at the cracking temperature of 450-600 ℃, and the chromatographic peaks of the cracked products are well separated without mutual interference.
Example 2 digestion reagent H 2 O 2 Selection of solution concentration
(1) A mixed standard soil sample is prepared according to the method of the step (1) of the example 1;
(2) Digestion conditions refer to step (2) of example 1, except that the volume concentrations of digestion reagents were changed to 1,5, 10, 20, and 30%;
(3) Weighing 20.00mg of mixed standard soil sample digested in the step (2) in a sample cup, performing Double-click pyrolysis-gas chromatography/mass spectrometry combined analysis according to the operation of the step (4) in the example 1 to obtain a total ion flow diagram of the PVC and PE mixed standard soil sample (Double-Shot-Py-GC/MS) under the action of digestion reagents with different concentrations, and inspecting the response of the characteristic peak of PVC and the characteristic peak of PE along with H 2 O 2 How the concentration varied, the results are shown in FIG. 4.
The results show that the concentration of the digestion reagent is an important factor influencing the digestion efficiency. H 2 O 2 The concentration of (2) can eliminate PE in the soil, and the subsequent quantitative analysis is influenced; h 2 O 2 Too low a concentration may result in incomplete digestion of organic matter in the soil, and the cracked product of the soil organic matter interferes with analysis of the MP-characteristic cracked product. By investigating the volume concentrations as 1,5, 10, 20 and 30% H 2 O 2 The digestion efficiency of organic substances in the solution is shown in FIG. 4, which shows that the solution is concentratedWhen the degree is 5%, the digestion of organic matters in the soil is relatively complete, and the response of the characteristic peak of PVC and the characteristic peak of PE follows H 2 O 2 The concentration increased and decreased, and in summary, 5% was H 2 O 2 Optimum digestion concentration of the solution.
Example 3 selection of digestion temperature
(1) A mixed standard soil sample is prepared according to the method of the step (1) of the example 1;
(2) Digestion conditions reference step (2) of example 1, except that digestion temperatures were changed to 30, 50 and 70 ℃;
(3) Weighing 20.00mg of the mixed standard soil sample digested in the step (2) in a sample cup, performing Double-click pyrolysis-gas chromatography/mass spectrometry combined analysis according to the operation of the step (4) in the example 1 to obtain a total ion flow diagram of the PVC and PE mixed standard soil sample (Double-Shot-Py-GC/MS) under the action of different digestion temperatures, and observing how the response of the characteristic peak of PVC and the characteristic peak of PE changes along with the digestion temperatures, wherein the result is shown in FIG. 5.
The results show that the digestion reaction temperature is over-high to promote H 2 O 2 When the solution is used for digesting PE, the digestion of organic matters is incomplete when the solution is too low. By examining the digestion conditions of the soil organic matters at the digestion temperatures of 30, 50 and 70 ℃, the results in fig. 5 show that at the digestion temperature of 30 ℃, the soil organic matters are basically completely digested, the response signal of the cracked product is low, the temperature has no great influence on the digestion effect of the soil organic matters, the influence on the response signal of the PVC characteristic cracked product is small, the loss of the PE characteristic cracked product is increased along with the increase of the temperature, and therefore the digestion temperature is set to 30 ℃.
Example 4 selection of digestion time
(1) A mixed standard soil sample is prepared according to the method of the step (1) of the example 1;
(2) Digestion conditions reference step (2) of example 1, except that digestion times were changed to 20, 40 and 60min;
(3) Weighing 20.00mg of mixed standard soil samples digested in the step (2) in a sample cup, performing Double-click cracking-gas chromatography/mass spectrometry combined analysis according to the operation of the step (4) in the example 1 to obtain a total ion flow diagram of the PVC and PE mixed standard soil samples (Double-Shot-Py-GC/MS) under different digestion times, and observing how the responses of the characteristic peaks of PVC and PE change along with the digestion temperature, wherein the result is shown in FIG. 5.
The results show that the digestion time directly reflects the simplicity and convenience of pretreatment and the experimental efficiency, and by observing the soil digestion results when the digestion time is 20min, 40 min and 60min, fig. 6 shows that the digestion effects of the three times on soil organic matters are similar, and different digestion times have small influence on the signal response of the characteristic product of MP, so that the 20min digestion time is selected.
EXAMPLE 5 examination of the methodology
(1) Instruments and reagents
Gas chromatography-mass spectrometry instrument (SHMADZU GCMS-QP2010 SE), cracker (Frontier PY-3030D). PE and soil mixtures and PVC and soil mixtures.
(2) Sample preparation
Preparing a mixed standard soil sample: preparing a mixed standard soil sample with the mass concentration of both PVC and PE of 2.00% by an equivalent soil dilution method, and gradually diluting the mixed standard soil sample with the mass concentration of both PVC and PE of 1.60%, 1.20%, 0.80%, 0.40% and 0.10% by the equivalent soil dilution method.
Preparing a simulated soil sample: the mixed standard soil samples with the mass concentrations of PVC and PE of 1.00% (simulation sample 2), 0.80% (simulation sample 3), 0.50% (simulation sample 1) and 0.01% (simulation sample 4) are prepared by an equivalent soil dilution method.
(3) Double-Shot-Py-GC/MS instrument conditions
A cracker: the first stage is 380 ℃ and the second stage is 600 ℃; cracker/GC interface temperature: 300-320 ℃; sample inlet temperature: 320 ℃; a chromatographic column: rtx-5MS capillary chromatography column (30 m x 0.25mm i.d. x 0.25 μm,5% phenyl-95% polydimethylsiloxane); when the cracking temperature is 380 ℃, the temperature programming condition is as follows: maintaining the temperature at 40 deg.C for 2min, heating to 100 deg.C at 10 deg.C/min for 10min, heating to 320 deg.C at 20 deg.C/min for 15min; when the cracking temperature is 600 ℃, the temperature programming condition is as follows: maintaining at 40 deg.C for 2min; heating to 320 deg.C at 20 deg.C/min, and maintaining for 15min; the split ratio is as follows: 50:1; the carrier gas is high-purity helium, and the column flow is as follows: 1mL/min; an ion source: EI; ion source temperature: 220 ℃; transmission line temperature: 250 ℃; electron energy 70eV; scanning mode: full scanning; scanning period: 0.5s; scanning range: m/z:50-600amu.
(4) Double-Shot-Py-GC/MS analysis
Weighing 500.00mg of the mixed standard soil sample into sample bottles, adding 5.0mL of 5% H 2 O 2 Digesting the solution at 30 ℃, reacting for 20min, heating to 100 ℃, drying for 5h, and removing the residual digestion reagent and the generated water. After digestion, the sample is put into a mortar and ground into powder for later use.
Determination of PVC: weighing 20.00mg of digested mixed standard soil sample, placing the sample in a cup, covering a layer of quartz cotton on the sample, fixing the sample cup on a sample rod, loading the sample cup into a cracker, wherein the cracking temperature is 380 ℃, pushing down the sample rod after the instrument is stabilized, enabling the sample cup to enter a heating zone of the cracker, and simultaneously starting a gas chromatograph for GC/MS analysis.
Determination of PE: after the low-temperature detection is finished, the sample cup is lifted, the temperature of the cracker is raised to 600 ℃, after the instrument is stabilized, the sample rod is pushed down, the sample cup enters a heating zone of the cracker, and simultaneously, the gas chromatograph is started to carry out Py-GC/MS detection with the cracking temperature of 600 ℃, and the operation is repeated for 3 times.
(5) Results and discussion
A standard curve is established by taking the concentration of MP in a soil sample (PVC is 0.10%, 0.40%, 0.80%, 1.20%, 1.60%, 2.00%, PE is 0.40%, 0.80%, 1.20%, 1.60%, 2.00%) as an abscissa and the peak areas of PVC characteristic cracking products (benzene, naphthalene) and PE characteristic cracking products (C19, C20, C21, C22) as ordinates. The experimental results are shown in Table 1, the linearity of the PVC characteristic product in the range of 0.10-2.00% of PVC mass concentration is good, R 2 Greater than 0.9857, detection limit and quantification limit are both 0.1mg/g; the PE characteristic product has good linearity within the range of the PE mass concentration of 0.40-2.00%, R 2 More than 0.9809, RSD less than 22.44%, detection limit and quantification limit of 2mg/g and 4mg/g.
TABLE 1 Linear equation, correlation coefficient, reproducibility, detection limit and quantification limit of characteristic PVC peak
The soil samples with the mass concentration of 0.40% are subjected to the 6-time parallel measurement in the day and the 2-time parallel measurement in each three-day, the reproducibility of the method is considered, the experimental results are shown in the table 2, and the RSD (n = 6) in the day and the day is 10.64-21.5%.
The established method is adopted to carry out MP quantitative analysis on the simulated soil sample, and the experimental result is shown in Table 3. To verify the accuracy of the method, the spiking recovery test was performed on sample 3, and the results are shown in Table 4, with the spiking recovery being 97.67-122.57%. The results of the above-mentioned experiments show that the method has good accuracy and can be used for determining the content of PVC and PE in soil.
TABLE 2 Intra-day and Interday precision of characteristic PVC and PE products
TABLE 3 determination of PVC and PE content in simulated samples
TABLE 4 recovery of PVC and PE on a standard basis
Claims (8)
1. A Py-GC/MS analysis method for micro plastics in agricultural soil, wherein the micro plastics are PE and PVC, and the Py-GC/MS analysis method comprises the following steps:
(1) Digestion of soil sample to be tested
Taking a soil sample to be detected, and adding H with the volume concentration of 1-30 percent 2 O 2 Digesting the aqueous solution at 30-70 ℃, heating and drying to remove the residual digestion reagent and generated water after the reaction is completed, placing the sample in a mortar after digestion, and grinding into powder for later use;
(2) Double-click cracking-gas chromatography/mass spectrometry combined method
Putting the soil sample digested in the step (1) into a sample cup, covering a layer of quartz cotton on the sample, fixing the sample cup on a sample introduction rod, putting the sample cup into a cracker, wherein the cracking temperature is 380 ℃, pushing down the sample introduction rod after the instrument is stabilized, putting the sample cup into a heating zone of the cracker, and simultaneously starting a gas chromatograph to perform GC/MS analysis to obtain a Double-Shot-Py-GC/MS total ion flow graph of the soil sample at 380 ℃; after the analysis is finished, lifting the sample cup, heating the cracker to 600 ℃, pushing down a sample introduction rod after the instrument is stabilized, enabling the sample cup to enter a heating zone of the cracker, and simultaneously starting a gas chromatograph GC/MS (gas chromatography/mass spectrometry) for analysis to obtain a Double-Shot-Py-GC/MS total ion flow graph of the soil sample at 600 ℃;
Double-Shot-Py-GC/MS instrument conditions:
the instrument comprises: GCMS-QP2010SE gas chromatography-mass spectrometer; a cracker: the first stage is 380 ℃ and the second stage is 600 ℃; cracker/GC interface temperature: 300-320 ℃; sample inlet temperature: 300-320 ℃; and (3) chromatographic column: rtx-5MS capillary chromatographic column; when the cracking temperature is 380 ℃, the temperature programming condition is as follows: keeping the temperature at 40 ℃ for 2min initially, heating to 100 ℃ at 10 ℃/min, keeping the temperature for 10min, heating to 320 ℃ at 20 ℃/min, and keeping the temperature for 15min; when the cracking temperature is 600 ℃, the temperature programming condition is as follows: maintaining at 40 deg.C for 2min; 20. heating to 320 deg.C/min, and maintaining for 15min; the split ratio is as follows: 30-50:1; the carrier gas is high-purity helium, and the column flow is as follows: 1mL/min; an ion source: EI; ion source temperature: 220 to 250 ℃; transmission line temperature: 250. DEG C; electron energy 70eV; scanning mode: full scanning; scanning period: 0.5s; scanning range: m/z:50-600amu;
(3) Performing qualitative and/or quantitative analysis by using Double-Shot-Py-GC/MS total ion flow graph of the soil sample obtained in the step (2)
(1) Qualitative analysis
If the characteristic peaks of benzene and naphthalene appear on the Double-Shot-Py-GC/MS total ion flow graph of the soil sample at 380 ℃ obtained in the step (2), the soil sample contains PVC; if the Double-Shot-Py-GC/MS total ion flow graph of the soil sample at 600 ℃ obtained in the step (2) has characteristic peaks of C19, C20, C21 and C22, wherein Cn represents a hydrocarbon peak cluster with the carbon atom number n, and the soil sample contains PE;
(2) quantitative analysis
Preparing a series of mixed standard soil samples containing PE and PVC with concentration, and obtaining a Double-Shot-Py-GC/MS total ion flow graph of the mixed standard soil samples at 380 ℃ and 600 ℃ according to the operations of the steps (1) and (2); taking the concentration of PE in the mixed standard soil sample as a horizontal coordinate, taking peak areas of PE characteristic cracking products C19, C20, C21 and C22 in a Double-Shot-Py-GC/MS total ion flow graph of the mixed standard soil sample at 600 ℃ as a vertical coordinate to establish a standard curve, substituting the peak areas of C19, C20, C21 and C22 of the soil sample to be detected obtained in the step (2) into the standard curve to respectively obtain the PE concentrations obtained according to C19, C20, C21 and C22, and taking the average value of the four as the PE concentration in the soil sample to be detected; and (3) establishing a standard curve by taking the concentration of PVC in the mixed standard soil sample as a horizontal coordinate and taking the peak areas of the PVC characteristic cracking products benzene and naphthalene in the Double-Shot-Py-GC/MS total ion flow graph of the mixed standard soil sample at 380 ℃ as a vertical coordinate, substituting the peak areas of the benzene and the naphthalene of the soil sample to be detected obtained in the step (2) into the standard curve to respectively obtain the PVC concentrations obtained according to the benzene and the naphthalene, and taking the average value of the two concentrations as the PVC concentration in the soil sample to be detected.
2. The method for Py-GC/MS analysis of a micro-plastic in agricultural soil according to claim 1, wherein the conditions of the Double-Shot-Py-GC/MS instrument are as follows:
a cracker: the first stage is 380 ℃ and the second stage is 600 ℃; cracker/GC interface temperature: 320. DEG C; sample inlet temperature: 320. DEG C; a chromatographic column: rtx-5MS capillary chromatography column; when the cracking temperature is 380 ℃, the temperature programming condition is as follows: keeping the temperature at 40 ℃ for 2min initially, heating to 100 ℃ at 10 ℃/min, keeping the temperature for 10min, heating to 320 ℃ at 20 ℃/min, and keeping the temperature for 15min; when the cracking temperature is 600 ℃, the temperature programming condition is as follows: maintaining at 40 deg.C for 2min; 20. heating to 320 deg.C/min, and maintaining for 15min; the split ratio is as follows: 50:1; the carrier gas is high-purity helium, and the column flow is as follows: 1mL/min; an ion source: EI; ion source temperature: 220. DEG C; transmission line temperature: 250. DEG C; electron energy 70eV; scanning mode: full scanning; scanning period: 0.5s; scanning range: m/z:50-600amu.
3. The method for Py-GC/MS analysis of microplastics in agricultural soil according to claim 1 or 2, characterized in that the soil sample is pretreated before digestion: and (4) screening large-particle impurities including residual plants, drying to remove moisture, grinding and sieving for later use.
4. The method for Py-GC/MS analysis of a microplastic in agricultural soil according to claim 1 or 2, wherein: in step (1), H 2 O 2 The volume concentration of the aqueous solution was 5%.
5. The method for Py-GC/MS analysis of a microplastic in agricultural soil according to claim 1 or 2, wherein: in the step (1), the digestion temperature is 30 ℃.
6. The method for Py-GC/MS analysis of a microplastic in agricultural soil according to claim 1 or 2, wherein: in the step (1), the digestion time is 20min.
7. The method for Py-GC/MS analysis of a microplastic in agricultural soil according to claim 1 or 2, wherein: in step (1), H 2 O 2 The volume concentration of the aqueous solution is 5 percent, the digestion temperature is 30 ℃, and the digestion time is 20min.
8. The method for Py-GC/MS analysis of a microplastic in agricultural soil according to claim 1 or 2, wherein: the concrete preparation method of the mixed standard soil sample containing PE and PVC comprises the following steps: and (2) putting PVC particles and equal amount of blank soil into a mortar, grinding and uniformly mixing, adding PE particles into the mortar, grinding and uniformly mixing, adding a blank soil sample with the same amount as the sample in the mortar, grinding and uniformly mixing, gradually adding a blank soil sample with the same amount as the mixture in the previous mixing step, grinding and uniformly mixing, and finally preparing to obtain a series of mixed standard soil samples with concentration.
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